Scaling an object up and down in an animation?
If you have moved and rotated your object and only created Location and Rotation keyframes, without creating any Scale keyframe, the animation will take into account the first Scale keyframe it meets and the scale of the object won't change until it meets the next Scale keyframe. If you want to make sure that the scale is taken into account at frame X you should keyframe with LocRotScale (or LocScale or RotScale).